Is it possible to have too much head space in a Conical Fermenter??

I have a 15 gal. Minibrew conical Fermenter that I am going to be using for my 5 gallon batches. I am wondering if there is going to be an issue with too much head space and will it negatively affect the outcome of the fermenting of the Beer? I also have 3 clamps that I am planning to use to secure the lid

Second Question
I am also looking into the Thermowell Fermentation kit or some other means of maintaining the temp of the wort in the minibrew during the winter months. Is it safe to use the thermowell probe in the fermenter? Has anyone used the Fermwrap Heater with a Minibrew or Other Plastic Conical Fermenter?

TIA,

Zman

According to something I heard on The Session, yes, it is possible to have too much head space in your fermenter: it allows for a heavier layer of co2 to build up, and this extra pressure can have a negative impact on the yeast.

I brew with mini brew fermenters. i have 4 of them. Sometimes i get head space and i have never had one problem ever. I sometimes fill with CO2 when i dump some yeast but that is only sometimes. usually the yeast is done with it's cycle by the time you bleed yeast anyway..