Trying to meet pre and post boil gravity's

My first post after 6 biab brews! I'm convinced biab is a great technique and I'm determined not to give up.

my last brew readings where:
pre-boil target 1049, achieved 1040
post-boil target 1060, achieved 1044.
final gravity always hits the mark...about 1010-12.
grain bill of 6kg pale malt and .5 kg crystal 40l.

I strike at 67 and mash around 64-65 for an hour with 3-4 stirs of the mash.

my previous brew had .5 kg less pale malt and similar gravity readings occurred...i thought a little extra pale malt would generate more sugars and all would be well...hhmmm not the case.

my kit is a 50l stainless steel old keg fired by a 3 ring burner.

I started with 39.5l water. I loose 6L as my tap sits high in the kettle.  I'm yet to measure pre and post boil volumes but will do next brew.

i adjusted the brew efficiency to 60% and that set the targets to what i achieved....but that adjustment was a guess.

Can anyone suggest what I may be doing wrong.

many thanks

IMO, this is a two-step process.  First, you want to tell BSmith what to expect for the next brew.  If you got only 1.040 then you should use a EE% that predicts 1.040 on the next batch.  (All else equal.) 

The post-boil of 1.060 (from a preboil of 1.049) would be 11 points evaporation, and you got only four points (from 1.040 to 1.044), so you'd want to enter a much lower evaporation rate. 

These changes, over time, will eventually get BSmith to accurately predict your estimates based on your personal BIAG process, so you can brew the beer you have targeted. 

Part two would be trying to improve the performance of your process, and gradually telling BSmith those revised numbers as you show positive increases. 

Are you adjusting OG readings for temperature.  I ask this as a novice since I measured pre-boil gravity and it was very low compared to target, but using the BSmith hydrometer tab adjustments actually made the temperature corrected value higher than target; so I am assuming that all OG readings should be adjusted for temperature. This makes a massive difference, but you probably already knew all that, for which I apologise.