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

for i in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    ma=max(a)
    mi=min(a)
    if ma==mi: print(-1)
    else:
        if a[0]==ma and a[0]>a[1]: print(1)
        elif a[-1]==ma and a[-1]>a[-2]: print(n)
        else:
            for x in range(1,n-1):
                if a[x]==ma and (a[x-1]<ma or a[x+1]<ma):
                    print(x+1)
                    break
            
    
