IR ESA - Part Contribution based?

We have received our migration letter to UC. We have a joint claim, my partner gets the higher rates of PIP (care and mobility), I get Carers Allowance and we have a joint claim for IR ESA, my partner is in the Support Group. Our ESA has always been Income Related, it says it on all the paperwork, but about 3 years ago we where told it's Contributions based, topped up with Income Related. This came to light because we questioned why my partner was getting p60s from HMRC showing the amount of taxable benefit. It clearly states that IR ESA is non-taxable concerning tax payable to HMRC. The question though is what will our ESA become when we migrate to UC? We have no idea because we have no idea what type of ESA we are on now, all the paperwork says it is Income Related but according to the DWP it is Contributions based, topped up with Income Related, this has never really been a problem until now. I have downloaded the migration guide and it says on Page 10 that Contributory ESA is not a legacy benefit and so we should not get a migration notice, which is evidence that we are on IR ESA. But when reading your guide it says that Contributions ESA will become New Style ESA under UC. We have no idea what our IR ESA (which is apparently Contributions based ESA topped up with Income Related ESA) will become under UC? Any clarity would be appreciated please. I have read a lot of information but just dont have a clue. Thank you