qPCR Primer Product Size
 

I would like to compare the mRNA expression of 4 different receptors via Real-Time PCR. Does the product size of the qPCR primers have to be the same amongst all 4 primers? Or can they be random sizes and if so could I still quantitate the information they yield? I will be using the 2^-Delta Delta C(T) method.

For example:
Receptor 1 product = 100
Receptor 2 product = 100
Receptor 3 product = 100
Receptor 4 product = 100

or

For example:
Receptor 1 product = 106
Receptor 2 product = 150
Receptor 3 product = 111
Receptor 4 product = 100