In the attached module, the effect 2F 0A0 in order 0 channel 4 at row 30 should set a fairly slow tempo. In OpenMPT this instead gets converted to the IT effect F14 Set Tempo +4 bpm.

In my pending libxmp patch I use the S3M BPM effect (in libxmp, tempos <0x20 are filtered in the S3M loader instead of in the effect handler):

    case 0x2f:  /* 2F xxx Set Tempo */
        if (parm) {
            parm = (parm + 4) >> 3; /* round to nearest */
            CLAMP(parm, XMP_MIN_BPM, 255);
            e->fxt = FX_S3M_BPM;
            e->fxp = parm;
        } else {
            e->fxt = 0;
        }
        break;