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

T = int(input())
for t in range(T):
    n = int(input())
    x = [int(i) for i in input().split()]
    m = max(x)
    a = len(list(set(x)))
    ans =-1
    if a<=1:
        print(-1)
    else:
        for i in range(n-1):
            if x[i]==m and x[i+1]<m:
                ans=i
        if ans == -1:
            for i in range(1,n):
                if x[i]==m and x[i-1]<m:
                    ans = i
            
        print(ans+1)         
        