I'm happy to discuss with you about this question.
As Boulenger and Regan stated, (Greenwood used this diagnose) the premaxilla and the tooth pattern are diagnostic for the genus Platytaeniodus. It distinguishes Platytaeniodus from Haplochromis by a more stouter premaxilla and a wider dentigerous surface, It says "the alveolar surface of the premaxilla widening toward the pharynx, the band of teeth in the upper jaw horseshoe shaped.."
Grenwood stated:" posteriorly the teeth are arranged in several rows, so that the premaxillary tooth band is always clearly U shaped, with the arms at least as broad as the medial part. Broadening of the posterior alveolar surface is gradual and shows positive allometry with standard lenght....
tooth band in the lower jaw are more readily diagnostic and less subject to variation with absolute size than those of the premaxilla. In Platytaeniodus the mandibular teeth are confined to the anterior and antero-lateral portions of the dentary and are grouped into two broad and roughly pyriform patches, contiguous at the symphysis, posteriorly there is a short, single row of four to seven teeth lying between the ascending part of the ramus and the anterior tooth bands"
This is the genus Platytaeniodus diagnose( the teeth form, number of rows and structure are a part of the diagnose)
From what I observed in the dental pattern of H,sp"red tail sheller", there is 2 to 6 rows of unicuspids tooth with strongly recurved tips , with bicuspids and tricuspids tooth in the postero lateral rows( this lateral tooth are unicuspids in degeni). Also the cranial measurements showed that the pre orbital depht was arround 17-18% of the head lenght, the interorbital width was arround 27 % of the head lenght, the eye diameter ranged between 25-27 % of the head surface, all this measurements and the tooth form and organisation show for me that red tail is closer to Ptyochromis subgenus than to Platytaeniodus(the most important difference is in the tooth form, number of rows, dental oganisation, premaxilla and maxilla form, in red tail the dentigerous surface doesn't show the typical U pattern observed in Platytaeniodus).
fom what I saw in H.sp"red tail sheller" I can't say that it belongs to the Platytaeniodus genus, it is too far from the dental pattern, and jaws form(the upper jaw being a little longer than the inferior jaw in Platytaeniodus degeni, they are off equal lenght in red tail sheller) H.sp"red tail sheller" has some similarities with H.granti in the tooth forms, numbers of rows,dental organisation and cranial measurments.