Does BSNL 3G Download Speed Depend On Size Of File Being Downloaded?

BSNL 3G offers great surprizes to me every time I use it. I've made a new discovery which is apparently correct. BSNL 3G download speed varies according to the file size. I'm currently download uBuntu 10.10 which is close to 700 MB and I'm getting download speed of about 100 - 150 kbps. Just few minutes ago, I was getting 8 kbps while downloading Firefox which is just 13 MB.

Now, does that mean BSNL is encouraging us to download bigger files? Has anyone else made this observation?