art KB9MZ wrote:

Thus my major lobe needs to be robust between about 10 degtrees and 4
degrees to ensnare most of the communication.

I don't recall you stated which band but I'll assume 20 meters.
Assuming flat terrain (for your Indiana QTH), a single Yagi at 120'
(your maximum possible) would cover these angles best. 140' (or 2
wavelengths high if it is not 20m) would be the optimum heightl to
center your main lobe at 7 degrees.

Two stacked Yagis at 60' and 120' would be better than a single one at
120' or 140' for 4-10 degrees, but obviously this means more work and
expense.

If your terrain is not relatively flat, and if you are lucky to be on a
hill with a gentle slope in the direction of England, the optimum
height will be much less. However you would need to model this using
HFTA in the most recent Antenna Handbook or YT in older editions.

73, Bill W4ZV