Need SP players opinions.

[Grumbler]

More then one variable. Terrain and visibility range matters also. Unit count might be a better metric then points. There has to be enough room to move dispersed, yet you want to fight concentrated. So that means game length is important also. I try to avoid maps smaller then 100 x 100 because arty can dominate a smaller map regardless of what percentage is used.
I try to make the points great enough to buy formations that match the map size. Tactical training manuals give the frontage a formation should cover, but those same manuals are always being revised due to changes in equipment, tactics, etc. Plus modern Mechanized warfare isn't about 'frontage' but firepower and mobility. That throws off the manuals in the real world and doesn't help much in the SP world either .
I would say experience will help you decide what is best for you, except that might not be what is best for someone else.
The Player with the most ladder games likes HUGE battles. I'm playing 3 games against Jad now that have 20,000 points per side on 120 x 120 maps. Unit density has morphed into burning wreck density. One battle is set in '47 and I have a regiment of Panthers and Pattons. That was 130 some tanks when we started. Units were pretty cheap back in that period and 20K will buy a LOT of everything.