This is because the SDLT would have been making a greater tax effort and the block grant adjustment would have been adjusted to include that greater effort.
Y rheswm dros hyn yw y byddai treth dir y dreth stamp wedi bod yn gwneud mwy o ymdrech dreth ac y byddai'r addasiad i'r grant bloc wedi cael ei addasu i gynnwys yr ymdrech gynyddol honno.