Multi-chiplet integration supports design flexibility, heterogeneous integration, and high-performance packaging, but wafer-scale assemblies can develop thermomechanical deformation and localized stress during reflow. This study uses finite element analysis supported by thermocouple measurements and laser-displacement measurements to sequentially evaluate three chiplet configurations and four chiplet area-coverage cases for Configuration 2 (53%, 66%, 71%, and 75%) on an 8-inch Si wafer under a common thermal profile. The three configurations have equal area coverage but differ simultaneously in chiplet number, shape, aspect ratio, orientation, spacing, boundary length, spatial arrangement, and symmetry. The simulated heating response showed a maximum deviation of 2.96% from thermocouple measurements, while the simulated and experimental deformation profiles showed similar center-to-edge trends with a maximum error of 9.78%. Configuration 1 and Configuration 2 produced the lowest and highest edge Z-directional deformations of 4.40 and 6.80 µm, respectively. For the configuration comparison, the maximum principal stress increased from 1.1383 MPa for Configuration 1 to 1.7628 MPa for Configuration 2, while the corresponding interfacial shear stresses were 1.1042 and 1.4928 MPa, with Configuration 3 showing intermediate values of 1.2492 and 1.2583 MPa, respectively. Within the investigated Configuration 2 cases, increasing area coverage together with accompanying geometric changes increased maximum Z-directional deformation from 6.7717 to 7.4150 µm maximum principal stress from 1.7628 to 2.3275 MPa, and interfacial shear stress from 1.0085 to 1.8560 MPa. These findings provide case-specific insight into wafer-scale thermomechanical responses associated with chiplet geometry, layout, and area-coverage conditions, without attributing observed trends to any single geometric parameter.