I am not entirely sure what you mean by borrowers share - is that like the loan to value (LTV)?
Your "share" will have already increased if you are on a repayment mortgage (and if the house has increased in value it will have increased further, but you would have to get your house revalued to prove this).
So if you started out with a 5% deposit and borrowed 95% of the value of the house from the bank, then depending on how much you have repaid the LTV may have decreased from 95% to 93%, or 90% or whatever as you "buy your house back" from the bank with your repayments.
I am not sure if that is what you mean though, because I don't know how the LTV could be more than 100% (unless its negative equity) and you can't own more than 100% of your house.
Are you sure that they say "110%" and "150"?
If so, I hope someone more knowledgable than me will be along to help you.
If the figures are in brackets like 95%, 85%, 75% etc then
use your current mortgage balance compared to the value of the house to work out what your share now is. Then work out from that which "bracket" you fit into - eg, if you started on a 95% LTV and have reduced it to 90% LTV, then you will qualify for a 95% LTV interest rate if your bank offers it. If your bank offers different interest rates for 85% and 95%, but doesn't differentiate between 90% and 95% then you will only qualify for the higher, 95% LTV interest rate, if that makes sense.
The lower the LTV, the lower the interest rate should be because it is a safer bet for the bank.