1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

import math
def dtb(n): 
    return bin(n).replace("0b","")
def btd(n): 
    return int(n,2) 
t=int(input())
for k in range(t):
    n=int(input())
    a=list(map(int,input().split()))[:n]
    b=a[:]
    b.sort(reverse=True)
    if b[0]==b[n-1]:
        print(-1)
        continue
    for i in range(n):
        if i==0 and a[i]==b[0]:
            if a[i+1]!=a[i]:
                print(i+1)
                
                break
            else:
                continue
        if i==n-1 and a[i]==b[0]:
            if a[i-1]!=a[i]:
                print(i+1)
                break
            else:
                continue
        if a[i]==b[0]:
            if a[i-1]!=a[i] or a[i+1]!=a[i]:
                print(i+1)
                break
    
    