You need to break down the peat (I hope you're using sphagnum peat!) 'chunks' with your fingers or something before potting them into a crumbly mix. There would be lots of empty spaces and gaps in the mix which means that when you water it from above, the mix will just 'sink' down and it will seem as if you only filled half of the pot up!
It also means that when you water via the tray method, not much water will get to the roots and the plant may die from the lack of water.
Always after repotting, a good thing to do is to top water it once or twice so the mix settles around its roots.
Hope I helped!