Optimal Calling Range Based On These Conditions?

Anyone else by themselves with a deck of playing cards and sometimes create poker scenarios, or conditions for you to solve? No? Just me? All right then Optimal Calling Range Based On These Conditions?

Recently, I invented this "game" for practice and curiosity. What would be my "optimal" range here and how would I calculate this myself?

Conditions of this "game"/scenario:

I play Heads-up No Limit but (to make it tougher on me and not just "luck") I begin the game with 25% of all starting chips in play. If the game has 1,000 chips in play, then I begin with 250 and the opponent with 750. In this "game", the opponent:

from the Big Blind: ALWAYS checks to the Flop and then shoves All-in on the Flop

from the BTN (also SB in Heads-Up) ALWAYS completes and then shoves All-in on the Flop.

Note: Any bets by us are met with All-in re-raises (including preflop open-raises if we so chose).

What strategy should we (basically calling range) use here? Also how would any blinds or antes impact the strategy? The smaller blinds are (or antes if used), then the deeper stacked we might be essentially playing, but is that relevant to this scenario and if so, then how much?

For precision-sake, assuming starting stacks are Hero 250 vs Villain 750 (remember we begin with only 25% of chips in this "game") and blinds of 10/20 with 50 ante (huge ante I know, but I didn't want this "game" to take all day - just to see how this scenario would run), then what would our optimal calling/shoving range look like? Since the format is Heads-up and our opponent plays a pure strategy (not a mixed strategy where they take actions some percentage of the time, here each action occurs 100% of the time [shoving All-in on the Flop]), then I imagine there would be a mathematical range were could come up with to optimally solve this "game."

p.s. Maybe I've been reading too much about GTO and Nash Equilibrium lately Optimal Calling Range Based On These Conditions?
1st place finish at CardsChat 30 Day Course Freeroll (May 31, 2020). As my first ever CardsChat event, this one will always be special for me.