Unlimited Tonnage Upgrades

I have been doing my research concerning sea time requirements for upgrades. I have reviewed 46 cfr 11.402 and it states that half of the required sea time must be on vessels over 1600 tons to maintain no tonnage restrictions. So my question is can I use 10 months of service on vessels over 1600 and 2 months on a vessel of 150 tons to upgrade my 3rd mate unlimited to 2nd Mate Unlimited. And is that two months on the smaller vessel credited day for day.

Thank you in advance for any guidance.