It appears that 2.5 mm 1-piece implants are not too small for the lower incisors (Fig.10-12), especially the central one (Fig.11).  There may be perforation in the apical half of the lingual plate (L in Fig.10).

3 Implants for 4 Incisors Last Next Xin Wei, DDS, PhD, MS 1st edition 10/21/2018, last revision 04/16/2019