AND yet...
 -etha 1 -asm 2 -y compute -mode 2 -estale 1 -showdiff 1 -ftime 10 -rxboost 21 -strap POL4E3@2190,POL8M2@2215,POL8H1@2215,POL8H1@2200,POL8H1@2250 -mvddc 900 -cclock 1215,1300,1250,1235,1235 -cvddc 900 -estale 1 -mode 1 -lidag 3

is the following results...

AMD Cards available: 5
GPU #0: Ellesmere (Radeon RX 580 Series), 4096 MB available, 36 compute units (pci bus 1:0:0)
GPU #0 recognized as Radeon RX 480/580
GPU #1: Ellesmere (Radeon RX 590 Series), 8192 MB available, 36 compute units (pci bus 2:0:0)
GPU #1 recognized as Radeon RX 480/580
GPU #2: Ellesmere (Radeon RX 570 Series), 8192 MB available, 32 compute units (pci bus 4:0:0)
GPU #2 recognized as Radeon RX 470/570
GPU #3: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 5:0:0)
GPU #3 recognized as Radeon RX 480/580
GPU #4: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 6:0:0)
GPU #4 recognized as Radeon RX 480/580
POOL/SOLO version

GPU# 0 strap "POL4E3" is applied successfully, mclock 2190MHz
GPU# 0 -rxboost option is applied successfully
GPU# 1 strap "POL8M2" is applied successfully, mclock 2215MHz
GPU# 1 -rxboost option is applied successfully
GPU# 2 strap "POL8H1" is applied successfully, mclock 2215MHz
GPU# 2 -rxboost option is applied successfully
GPU# 3 strap "POL8H1" is applied successfully, mclock 2200MHz
GPU# 3 -rxboost option is applied successfully
GPU# 4 strap "POL8H1" is applied successfully, mclock 2250MHz
GPU# 4 -rxboost option is applied successfully

ETH: GPU0 33.125 Mh/s, GPU1 33.531 Mh/s, GPU2 33.381 Mh/s, GPU3 33.120 Mh/s, GPU4 33.531 Mh/s
GPU0 t=58C fan=59% P=68W, GPU1 t=49C fan=45% P=89W, GPU2 t=55C fan=49% P=76W, GPU3 t=53C fan=49% P=99W, GPU4 t=54C fan=39% P=71W

AND....
-mode 1 -asm 2 -estale 1 -showdiff 1 -gser 2 -etha 1 -rxboost 15,21 -strap POL8M2@2115,POL8H1@2150,POL4H1@2075,POL8S2@2150,POL8H4@2100 -mvddc 875 -cclock 1250 -cvddc 900 -lidag 3
Nets the following....

23:11:45:269   2308   AMD Cards available: 5
23:11:45:269   2308   GPU #0: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 1:0:0)
23:11:45:270   2308   GPU #0 recognized as Radeon RX 480/580
23:11:45:271   2308   GPU #1: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 5:0:0)
23:11:45:279   2308   GPU #1 recognized as Radeon RX 480/580
23:11:45:280   2308   GPU #2: Ellesmere (Radeon RX 580 Series), 4096 MB available, 36 compute units (pci bus 6:0:0)
23:11:45:295   2308   GPU #2 recognized as Radeon RX 480/580
23:11:45:299   2308   GPU #3: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 7:0:0)
23:11:45:300   2308   GPU #3 recognized as Radeon RX 480/580
23:11:45:301   2308   GPU #4: Ellesmere (Radeon RX 580 Series), 8192 MB available, 36 compute units (pci bus 8:0:0)
23:11:45:301   2308   GPU #4 recognized as Radeon RX 480/580
23:11:45:302   2308   POOL/SOLO version

23:11:50:932   2308   GPU# 0 strap "POL8M2" is applied successfully, mclock 2115MHz
23:11:50:959   2308   GPU# 0 -rxboost option is applied successfully
23:11:51:054   2308   GPU# 1 strap "POL8H1" is applied successfully, mclock 2150MHz
23:11:51:092   2308   GPU# 1 -rxboost option is applied successfully
23:11:51:189   2308   GPU# 2 strap "POL4H1" is applied successfully, mclock 2075MHz
23:11:51:199   2308   GPU# 2 -rxboost option is applied successfully
23:11:51:305   2308   GPU# 3 strap "POL8S2" is applied successfully, mclock 2150MHz
23:11:51:315   2308   GPU# 3 -rxboost option is applied successfully
23:11:51:413   2308   GPU# 4 strap "POL8H4" is applied successfully, mclock 2100MHz
23:11:51:421   2308   GPU# 4 -rxboost option is applied successfully

13:26:36:944   1550   ETH - Total Speed: 161.160 Mh/s, Total Shares: 4901, Rejected: 0, Time: 86:14
13:26:36:946   1550   ETH: GPU0 31.769 Mh/s, GPU1 32.496 Mh/s, GPU2 32.005 Mh/s, GPU3 33.046 Mh/s, GPU4 31.844 Mh/s

I bolded the 4 GB cards the first set is Elpida and the second set is Hynix.  As you can see the clock speeds turned down in whole group still gets above 32 Mhs. If i run the cards individually it'll go and hold 33/34 Mhs at 2200 and 2250.