OK, when I have completed my feet, which should be shortly, I will move the amplifier up to the middle of the cabinet, that should make the loading be the same on both drivers.
Based on my calculations the cabinet with no obstructions has an opening of 286 square inches. The piston area of both drivers is 152 square inches. The amplifier box covers about 130 square inches. 286 - 130 = 156 square inches of "covered space." Based on my limited understanding if the amplifier is moved to the middle it should cause little if any loading on the woofers.
Another little note about the my build. I built the cabinet based on the design on your site as accurately as my limited woodworking skills allows. I then wrapped that cabinet in a second cabinet that extends beyond by 3/4" on the front & back. The amplifier braces are attached to the outside edge of the original cabinet with 3/4" (1x2) oak, so the box that the amplifier is in is actually 3/4" behind the rear opening of the original cabinet. The point I am making is that the calculations above are more conservative than the reality.
Irrespective of all of this, in its current configuration with the KEFs as mid/tweeters, I happily listened to all of my test recordings as well as some new fun stuff, and am pleased with the results.
The first thing I test with is a Sheffield Drum CD, then I play a cut off a Hybrid CD called "Alone Together" which is female vocal with acoustic bass to verify that the bass sound is well defined through various frequencies. Then I fire up 3 O'clock blues from the "Riding with the King" CD. For fun I played some CDs I picked up at a garage sale called "Classical Thunder I & II."
I will A/B them against the B&W 802s soon.