I have tried this before giving 7-9 blues to the cryptarch at once around 2 or 3 times. I noticed that if you give them all together the rating drops from blue to green around the 4th or 5th engram you encode. I am not sure if this is going to be adressed in the next patch.
The reason I hoarded engrams was because I just used them to increase my cryptarch ranking hoping that I would get a purple engram in the mail.
If you plan on mass encoding be careful. This could also be RNGesus bending me over and fucking me, but I'd be safe and encode one at a time if you are actually planning on using the gear from engrams instead of scrapping it like I usually do.