If you've a large discretionary income present, it's fine to lump sum since the funds are available. Personally, I wouldn't lump sum with everything at once. I'll like to divide the money into 3 parts, lump sum with the first part, use the second part to increase my aggressiveness in DCA and keep the last part for buying my target dip.
The first and third parts are reasonable with me but I am not surely understand your point with the second part for aggressive in DCA. What's difference between aggressive DCA and dip purchases?
I see the purposes of second and third parts are quite similar as you can wait for dips and take such chances for abnormal purchases with bigger capital spent for each purchase than normal DCA in a first part. I consider action of spending bigger capital for Bitcoin purchase whenever you see dip as better DCA chances than other times is aggressive buying.
The discretionary income to be used depends on the level of your comfort and not even about the market environment and If you say buying on a Lump sum is worth while buying on the down side then to me you are describing buying the dip and not buying with the lump sum, because talking about buying with the lump sum has nothing to do with the market conditions but rather an investor decision to buy immediately with the available Lump sum amount irrespective of the market conditions,
If you have part of your income as Discretionary Investment Capital, it's like your spare money which is available for you in a long time without need of spending so that you are very comfortable in using this Discretionary Investment Capital for investment. It's more easy and comfortable to spend it for buying a very good investment asset like Bitcoin.
Your observation is very good, it would be best to only buy during dips, but isn't it better to always buy gradually and leave a portion of that discretionary income for dips? Because the DCA method can have a routine or specific dates to buy some BTC, but discretionary income in addition to some additional income can be used for that, for the dip as well, then we would be buying intelligently without stopping our DCA plan.
Buying dips is always nice experience as after dips, price recovers very strongly and it gives you very good short term profit. It causes amazing experience and happy feelings but the disadvantage of waiting for dips is it might take a very long waiting time, and you might miss many other DCA chances.