2.75% is a very low percentage of starter, I believe Varasano is using 40%, I think you'll see MUCH greater flavor with higer percentages, I've gone from 20% to 25% to 30% to 40%.
At one point, Jeff Varasano did use a lot of starter material. My recollection is that it was around 40%. However, he later very substantially reduced the amount, I believe during the exercise in which pftaylor and Jeff tried to recreate the Patsy's dough and devoted an entire thread to that exercise. If you are interested, I think you can find the shift to using less starter culture in the Patsy's Reverse Engineering thread at http://www.pizzamaking.com/forum/index.php/topic,1053.0.html
Marco (pizzanapoletana) recommends that the starter culture be used at very low levels, pretty much for only leavening purposes and for mild flavor contribution to the finished crust. His recommended amount is 1-5% of the weight of the formula water (not formula flour). The high end of that range would typically apply in the winter where more starter is needed to counteract cooler temperatures, and the low end of the range would typically apply in the summer where less starter is needed because of the warmer temperatures. This, of course, is all with respect to room temperature fermentation as is used in Naples. Once you get to preferment levels, such as you are using, then there are other effects that are imparted to the dough, including higher acidity levels and gluten tightening effects, and quite possibly various kinds of crust flavors. Marco would argue that you are making bread dough at those levels, not pizza dough. For example, see Marco's reply to one of my posts on this point, at Reply 20 at http://www.pizzamaking.com/forum/index.php/topic,3153.msg26814.html#msg26814
Al (artigiano) did not indicate whether his 2.75% starter is with respect to the weight of formula water or with respect to the weight of the formula flour, but either way I think his usage is not in the preferment range but in the leavening-only range.