problem with assembly code after rewriting with 16bit

Question

I've had an assembly (MASM x86) code for doing this C++ equation

void main()
{
unsigned int i, B[10], A[10]={3,2,3,1,7,5,0,8,9,2}; 
for (i=0; i<10; i++){
B[i] = A[i] + 2 * (2*i + ( (3*i+1) / 5) );
}

it's working when I use 32bit registers and variables but after changing them to use 16bit it returns some errors.

The assembly code

.386  ; Specify instruction set
.model flat, stdcall  ; Flat memory model, std. calling convention
.stack 4096 ; Reserve stack space
ExitProcess PROTO, dwExitCode: WORD  ; Exit process prototype

.data
    A WORD  3,2,3,1,7,5,0,8,9,2  
    B WORD  10 DUP (?)                    
                            
    var1 WORD 0
    quotient WORD 0

 ; A[i] + 2 * (2*i + ( (3*i+1) / 5) )
.code      
main PROC
    mov si, 0                  

loop_start:

    ;(3*i+1)
    mov ax, 3                    
    mul si                      
    inc ax                   
    
    ; / 5)
    mov dx,0   
    mov cx,5
    div cx    
    mov quotient,ax

    ; 2*i
    mov ax,2                           
    mul si     

    ; (2*i + ( (3*i+1) / 5) )
    mov bx, quotient
    add ax,bx
   
   ; 2 * (2*i + ( (3*i+1) / 5) )
   mov var1,2
   mul var1
   mov var1, ax
  
    ; load array A
    lea bx,A
    mov cx,4

    ;A[i] + 2 * (2*i + ( (3*i+1) / 5) )
    ;imul dx,si 
    ;mov bx, dx
    mov ax,[bx + TYPE A * si]
    add bx,var1
   
   ;load array B and store
    lea ax,B
    mov  [ax + dx], bx

    ; i<10; i++
    inc si                   
    cmp si, 10                 
    jl loop_start  

INVOKE ExitProcess, 0 ; call exit function
  
main ENDP ; exit main procedure
END main  ; stop assembling

The error I'm getting is error A2031: Must be index or base register on mov ax,[bx + TYPE A * si] when I'm trying to read array index

As far as I know the bx is a base registry, I also add bx with si outside of the [] but still doesn't work!

Update

Is there anyway to run fix this code without using 32bit indexes, registers and variables?