Used my bivy kit for the first time last night, Skyhigh600, hunka, and tarp.

I got quite hot so must of been sweating quite a bit as there was some damp inside the bag this morning, not much.

I did notice that my feet were touching the tarp and that the foot box was a bit more damp than the rest of the bag. Will the bivy bag touching the tarp allow for water to get in?

Yep. Got soaked one night in the peaks when a sheep decided to use my tent as a wind break, pressing the sheet against me. I woke up in the morning soaked where it had touched

It shouldn’t do, if you’ve a goretex Bivi bag surely?
Difference in a tent is the inner isn’t made of a waterproof material..

Never got wet in a gortex bivvy under a tarp. And I used to do it for a living (so lots).

A bivi should be waterproof, that’s the whole point.

However if something puts pressure on a particular part of it then it might cause more condensation to be a problem in that spot.

I try and keep the tarp high enough to allow a fair bit of air flow, unless the weather is really wild.

Few options here – http://www.bikeandbivi.co.uk/php/viewtopic.php?f=2&t=11

Condensation is your enemy in the bivi bag. If you’re under a tarp then you don’t need to fully close your bivi bag. If the bag is fully closed then you’re more likely to get condensation – this can be a nightmate with a down sleeping bag
The better quality bivi bags suffer less from condensation as the moisture transfer thru the membrane is better, so proprietry fabrics like AlpKit won’t be as effective as eVent or GoreTex.
IF you get ventilated then you can reduce condensation quite a lot

If you’re hot (possibly sweating) in your bivvy bag then there’s a good chance condensation wll form inside. As said the problem will be eased if you use an eVent or Goretex bag but the condensation can still be present. I’ve always found it worse at the foot end … perhaps this is due to, the bag being smaller there so having less surface area to breath or it’s the part furthest away from the big hole at the top where your head is.

Either way, what you’ve experienced is condensation not leaking.

Most bags dont have full length zips so I can see condensation being an issues if the bag is quite a snug fit. I use Rab bags that are made from pertex endurance so they have a little better water resistance.

In my case, it was a sleeping bag in a normal tent.