Lacking published FR and polar plots for 511E/288, assuming they're the same as a 511B/802 on the bottom end is... well... an assumption.

Same for selecting an XO point before deciding on LF cab(s). You're seeking a near polar match for the LF/MF at XO. With the LF narrowing as F rises and MF widening as F lowers, there's gonna be a sweet spot where they ~match*.

(Besides, we all wanna see some 511E/288 plots)...:coffeedrinker:

Brainfurt; was there one in the old tech letters?

*Same goes for the MF/HF XO.