weird affects with less caps

    I have tryed a few things with my 7" coil and found out wierd things that 
I don't remember anyone mentioning. My transfomers add up to 12kv/90mA (3- 
12/30's NSTs) and my secondary 7 x 21" 24 gauge. According to many programs, 
my primary should be tapped at 13 1/4 turns.
    Since I lack meters and such, I had an idea. Instead of keeping my caps ( 
15 beer bottles) and changing the tap, I kept a 13 1/4 turn tap and added and 
subtracted caps. I know I am supposed to have .019uF, but my bottles are way 
short of that - just a guess. I found that when I have 10 bottles, I get the 
longest spark ~19" with the fixed tap point, definitely not what I expected. 
The type of spark changed with 5 bottles, it was a 14" ARC of white, instead 
of purple branches about 24-30" with 15 bottles and a 10 turn tap (my old 
setup). Then, when I take away even more caps, two or one left, the coil 
output resembles the arc out of my NSTs, less hot though, maybe arcing 2" 
talland 5" long! 

    Is there an explaination for this? Also, could this experimenting be bad 
for my coil? Is there more wattage in my secondary with my 2 bottle setup? My 
coil heats after a few minutes, never happened before...

Thanks in advance,