Most recent LT test. Mixed results

I ran another LT field test yesterday afternoon. It has been about 4 months
since the last test. I have seen great improvements. This most recent test,
My pace for the overall test was almost 1min/mile faster than my last test, and
my avg HR is 5 bpm's lower. So....Ive re-calculated my zones.

Here is what is strange to me. My runs that have been between 3 to 6 miles in Z1-2,
I have been able to hold a pace of ~9:35, and by the end of the run, I am at the
bottom to mid Z 2. On my longer runs, I usually start at a 10:00 mile pace, but it
seems like my HR gets up near the top of Z2 by mile 4 or 5. Now with my new Zones,
I will have to run an 11:00 min mile pace to keep my HR low. That does not seem
right, if I am able to run faster at a lower HR.

I really hate running slow because it just does not feel right. Could it possibly be
that my form is more efficient when I am running at a faster pace? Could it be that
I just need to get in more slow runs (really slow) at longer distances?

Any advice would be appreciated.