A little excess Starsan won't make a difference in that sense.
How long have the bottles been carbonating? If they have been in the bottle for just a week or two it could be that the gas is foaming out because it isn't comfortably dissolved into the beer yet.
Is the poured beer still quite fizzy? Or does it end up a bit flat after gushing?
You can accelerate getting the CO2 to adequately dissolve by putting the bottle in the fridge for a few days. However, if there is an uneven distribution then there is no way to tell if that is what is going on until you've opened a good number of the bottles.
Sometimes, I've found that I get more trub in the bottles just due to the yeast - I'll never use the Yeast with Youngs kits again unless I can put my full fermenter in the fridge, because I can't get the yeast to settle out nicely, even after a month; they just like swimming, and so my its harder for friends to pour the homebrew too without getting some yeast in their glass. With Safale S-04 on the other hand, there was a tiny film of yeast at the bottom of each bottle and it stuck there even after tipping the bottle upside down; this is without using a bottling bucket too - I add a solution of sugar to the primary at 3 weeks, and stir with a slotted spatula, being careful not to rouse up too much yeast. I only stir for a minute or so, and I try to blend the middle volume of the beer by moving the spatula through it back and forth firmly, rather than spinning the beer up at all as this will bring up some trub. Half an hour later, I bottle; never had problems with distribution of sugar/carbonation (In fact, its more even than it was when I was putting a teaspoon of sugar in every bottle as my first kit recommended - total P.I.T.A, sugar everywhere
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I wonder if the yeast are assisting me in spreading the sugar solution around in that half hour...