Can you please clarify the stamp duty element and why it is so high? (HPS/HPSS)

How is my Stamp Duty Land Tax (SDLT) calculated? | Help (pfida.com)

We enter the partnership so you can buy your home and as PLC already owns other properties that are then leased to our customers, despite regularly challenging this, HMRC view this in the same light as a Portfolio Buy-to-Let purchase, which is the reason for the Stamp Duty payment being higher. We ask you to cover this otherwise, we are entering the agreement at a loss, which would impact our other investors and would not make it financially viable to support your home purchase. Once you have purchased all the shares in the home, we will transfer the title deeds to you. The amount of Stamp Duty due at the time of completion will be set by HMRC and we are unable to advise on any taxation queries. You may wish to get independent advice.