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