As your question is similar to what I have in my mind, I want to add:
How does the WP (8.1 or Silverlight) scaling system works for different phone sizes (eg 520 vs 1520)?
eg. sip keyboard height 8.1 SL is 339 px in phones below 4.7 inch but a scale factor is applied for larger phones. How to determine the scale factor? Have seen that it depends on the physical display size rather than resolution. How to determine the scale
factor which multiplied by 339 will give the keyboard height in larger phones?