In FTGU we learn that typically an Ace high flop favours the Preflop raiser and middling flops favour the caller. But by how much?

I've been doing some calculations using range chart ranges and got surprising results. For example, using a CO open range vs a BTN calling range, on a flop of As7d5d I've found the CO range to have only 47.77% equity.
I got to this figure by simulating all CO open hands vs all BTN calling hands and counting the wins/draws/losses for all possible runouts after the flop. Then I take (wins + (draws/2))/total runouts.
On a flop of 8h7h6c, CO equity comes out as 47.54%.
Should I be seeing much bigger differences between equity of ranges for these different flops as I expect?
The range charts are from a reputable source which I won't mention.
Is this a surprising result to you as it is to me? Are there any existing free tools that calculate equity for competing ranges so I can check my own program is working correctly?

Thanks