Invalid Premise #1 is "full BTC refund means the EXACT NUMBER of BTC paid NO MATTER WHAT"
Ok, at exactly what BTC price was the full BTC refund clause valid? You can show that, can't you? Or is the price restriction just a figment of your sick imagination?
"Full BTC refund" means you get a full refund (of the USD purchase price) in BTC. At whatever the rate happens to be at the time. Obviously.
If you paid with X dollars worth of BTC, you get X dollars worth of BTC should a refund come due.
The 'I'm entitled to get back the exact same number of BTC from HF, no matter the economic impossibility of such an expectation when the price of BTC rises almost tenfold" point of view is very popular here. It exists in many peoples' imaginations, but cannot be reconciled with reality.