RTFM, I am sorry but there are lots of misconceptions in this thread.

In the first order, the stability of any two surface airplane (whatever the relative dimensions of the fore and aft wings are) is a function of:

1. CG position,

2. size and relative position of the two wings wrt CG

3. the ratio of the lift slope of the two surfaces(which in turn is a function of AR)

However It is not a function of the incidence of the surfaces wrt to the fuselage. IOW changing the relative incidences, in the first order, will not make an otherwise stable airplane unstable or visa versa. This is an important concept to fully understand. Otherwise you can talk yourself round in circles and try to fix phantom problems.

In the first order, the control range (speed range) is a function of the relative incidence range of the surfaces. You can change the fore wing incidence or the rear wing incidence or both. You can decrease the speed by either increasing the incidence of the fore wing or decreasing the incidence of the aft wing or some combination of the two.

In fact, the fastest a Flea with a fixed rear wing set at 6 degrees can safely fly is the speed at which the front wing reaches 6 degrees to maintain level flight.

Any faster, and the front wing incidence will need to be decreased, and the rear wing will start "overpowering" the front, so the stick will need to be pulled back to bring the nose up again.

It should be clear now this cannot be true. There is nothing special about how any stable flea derivative flys. When you reach the end of the fore stick control range you cannot go any faster. That is the fastest speed you can fly. It will not suddenly dive because of some underlying peculiarity of the flea configuration relating to rear wing overpowering the fore wing and relative incidence. Of course this assumes the flea is stable to begin with (some of the early fleas where not). Also there are some second order factors that are more relevant in flea type designs but this does nor preclude from the above principle.

If you are not satisfied with this description, I would recommend building a spreadsheet to calculate the pitch equilibrium of a flea design. You will find it very illuminating and will uncover many of the misconceptions in this thread. If you have already done this and found it to support your theory then please share your spreadsheet and I will be happy to review and correct it for you. The basics of FW stability have been very well understood for about a century.