To slow the thing down - add wing area -(and stab area)
this added wetted area also can produce more induced drag -which is what really slows things down
a bit more fuselage does little in that respect.
as for being too light to snap- No way .
get out the Depron and do some fast building and testing .
we have done stuff with flat wings - that fly - honest -as smoothly as any pattern plane and snap in the blink of an eye -and hold heading perfectly.
The little Knuffel design is really a flat plate rip off of current Europan FAI pattern stuff.
The past year spent building and destroying these things has been the most informational period -regarding what really happens - I have ever spent.
Now I have to go back and redesign my big stuff- --lower weight - more power - slower flight
Funny but it takes MORE power to fly well at slower speeds .